As the care of injured patients has evolved and improved, various organ systems have in turn been the limiting factor affecting recovery after a severe injury or major operation. Although patients after operation or injury may die from a number of specific or general injuries and complications, there has usually been, at any one time in surgical history, a particular organ system that has been the most common and difficult problem. The major wars have provided larger experience and more concentrated documentation of what was happening simultaneously in civilian hospitals to patients traumatized by injury or operation. In the 1930s and during the early part of World War II, the major organ system that limited survival after injury was the cardiovascular apparatus (shock), even when that system was previously normal. An understanding of blood loss, the requirements of whole blood replacement for hypovolemia, and the nature of traumatic or wound